UC Merced

Hepatitis C virus (HCV) is a major health problem which is affecting more than 170 million people worldwide. About 80% of HCV-infected patients develop chronic infections because they cannot clear the virus. Chronic infections increase the risks of progressing to severe liver diseases such as cirrhosis and hepatocellular carcinoma. HCV has several strategies to evade host interferon (IFN) responses. In this study, we hypothesize that a novel HCV viral protein, frameshift/alternate reading frame protein (F/ARFP) from HCV -2/+1 frame, contributes to the suppression of retinoic-acid-inducible gene-I (RIG-I)-mediated IFN induction. We found that F/ARFP suppressed type I IFN induction stimulated by HCV RNA pathogen-associated molecular pattern (PAMP) and synthetic double stranded RNA poly(IC). This suppression occurred independently of other HCV viral factors such as nonstructural protein NS3/4A. Point mutations in the full-length HCV sequence for introducing premature termination codons in the -2/+1 frame enhanced type I IFN induction. Taken together, we suggest that HCV F/ARFP suppresses type I IFN responses mediated by RIG-I. Additionally, we investigated the role of NAD(P)H oxidases (Noxs) in type I IFN pathway. Nox family enzymes function as important sources of regulated production of reactive oxygen species in cell signaling and regulation of gene expression. However, much remains to be investigated how Nox enzymes contribute to the immune response against virus infection. In this study, among seven members of Nox family, we hypothesize that Nox1 has a role in type I IFN pathway. We observed that the mRNA levels of Nox enzymes including Nox1, Nox4, Nox5, Duox1, and Duox2 were elevated by poly(IC). We showed that poly(IC)-triggered IFNβ1 mRNA induction was suppressed by DPI, a flavoprotein inhibitor, in Huh7 hepatoma cells. Further study suggested that Nox1 siRNA-transfected Huh7 cells decreased poly(IC)-stimulated IFNβ1 mRNA induction in Huh7 cells. Moreover, HCV replication was increased by Nox1 and Nox4 knockdown by corresponding siRNAs. Taken together, these data suggest that Nox1 may modulate type I IFN pathway. Therefore, our study may provide new insights into how HCV evades the host innate immune response and how Nox enzymes function as antiviral agents and points to possible new drug target for therapy.